The present invention relates to steering wheel absolute angular position sensors.
In many applications, including motor vehicles, it can be important to know the absolute angular position of a rotating body. As but one example, when starting a motor vehicle, it may sometimes be necessary to know which steering revolution the steering wheel is in instantly at power up. Not only does this allow the driver to know which way the front wheels are directed before placing the vehicle into gear, but some computerized vehicle control systems might require knowing the steering position as well. For example, in an automated steering system, such as a steer-by-wire system, the control system must know the position of the steering wheel at all times in order to control the direction of the vehicle. Not only must these systems know the position of the steering wheel, they must know in which revolution the steering wheel is in at the time of measurement.
One such device includes a relatively large input gear installed on the steering shaft. The input gear is meshed with a relatively small output gear. A first magnetic field sensor and a second magnetic field sensor are placed near the input gear and the output gear, respectively. The gears are constructed so that as they rotate the angular position of the gears is sensed by the sensors. The ratio of the input gear to the output gear is chosen so that the gears are out of phase as they rotate through multiple revolutions. The signals from the sensors are used to determine the absolute position of the steering shaft. The second sensor provides a relatively accurate, high resolution signal representing the angular position of the output gear. This signal, used in conjunction with the out-of-phase angular position signal from the first sensor is used to determine which revolution the steering shaft is in when the signal is received from the second sensor. Thus, the absolute position of the steering shaft is known.
Theoretically, the angular position of the output gear is equal to the angular position of the input gear multiplied by the gear ratio. However, since the large input gear is installed on the steering shaft, the signal from the first sensor can be adversely effected by mechanical noise caused by slight lateral motion of the steering shaft, i.e., wobble. Moreover, the signal from the first sensor can be adversely effected by temperature changes, material magnetic hysteresis, and electrical noise. As recognized by the present invention, if the error in the signal is outside a predetermined range of tolerances, a microprocessor connected to the sensors will incorrectly determine which revolution the input gear is in when the signal is received. Thus, the microprocessor will incorrectly determine the absolute angular position of the steering shaft.
The present invention has recognized these prior art drawbacks, and has provided the below-disclosed solutions to one or more of the prior art deficiencies.
A method for determining an absolute position of a rotating shaft includes determining an angular position compensation value. Then, the absolute angular position of the rotating shaft is determined based on the angular position compensation value. Preferably, an adjusted angular position of an input gear that is connected to the rotating shaft is determined based on the angular position compensation value. The absolute angular position of the rotating shaft is then determined based on the adjusted angular position of the input gear.
In a preferred embodiment, the angular position compensation value is determined for a revolution N+1 by determining an angular position of the rotating shaft for a revolution N. Also, an angular position of the input gear for the revolution N is determined. Preferably, the angular position compensation value for the revolution N+1 is determined as APCVN+1=(APRSNxe2x88x92AAPIGN)/xcex1+APCVN, wherein APCVN+1 is the angular position compensation value for the revolution N+1, APRSN is the angular position of the rotating shaft for the revolution N, AAPIGN is the adjusted angular position of the input gear for the revolution N, xcex1 is a compensation factor that is greater than one, and APCVN is angular position compensation value for the revolution N.
In a preferred embodiment, the method includes determining if the angular position compensation value is greater than a predetermined maximum threshold. If so, the angular position compensation value is established so that is equal to the predetermined maximum threshold. Moreover, it is determined if the angular position compensation value is less than a predetermined minimum threshold. If so, the angular position compensation value is established so that is equal to the predetermined minimum threshold.
In another aspect of the present invention, a vehicle control system includes an absolute angular position sensor assembly and a microprocessor connected to the sensor assembly. In this aspect, the microprocessor includes a program for adjusting a signal representative of an absolute position of a rotating shaft.
In still another aspect of the present invention, a method for determining an absolute position of a rotating shaft includes providing an input gear and providing an output gear. An angular position compensation value is determined. Moreover, an adjusted angular position of the input gear is determined based on the angular position compensation value. Then, the absolute position of the rotating shaft is determined based on the adjusted angular position of the input gear.
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: